Counting circuits



Feb.. 3, 1959 A. DAvlsoN Er AL couNTING CIRCUITS` original Fileduan. 25', 1955 Inuenlbfr.- ALAN DAV/50N RONALD THREADGULD United States Patent 2,872,619 'COUNTING CIRCUITS Alan Davison and Ronald Threadgold, Liverpool, England, assignors `to Automatic Telephone & Electric 'Company Limited, Liverpool, England, a British com- Pally This application is divided from our copending application No. 483,985, led on January 25, 1955, now U. S. Patent No. 2,850,718.

The present invention relates to pulse counting circuits and is particularly concerned with circuits employing va chain of gas-filled discharge tubes adapted to be rendered conducting successively and tobe rendered non-conduct-v` ing successively.

Countersof this type are already known in which a connection is made from the cathode of one counting tubev to the trigger electrode of the next tube in the chain. The tiring of one tube raises the potential of its cathode and consequently primes the lfollowing tube. A

common pulse source applies pulses to the triggerelec-v vtrodes of all the tubes in the chain simultaneously, but

only the tube which is primed res on receipt vof a pulse,

and the tubes, therefore, are vtired successively.

It is usual in counter circuits of this type to include a capacitor in the cathode load of each tube and to connect the anodes to a positive voltage source through a common resistor. By this arrangement the tiring of one tube can be made to extinguish the previously conducting tube by increasing the voltage drop across the common resistor.

y The charge on the capacitor in thecathode circuit of the already conducting tube causes the voltage betweeny anode land cathode of this tube to be less than the dischargemaintaining voltage for the tube, while the capacitor in the cathode circuit of the primed tube is uncharged, and the anode/ cathode voltage of this tube is still suicient to enable it to strike.

Counter circuits of this type have several disadvantages.

ger electrode must conform to a fairly critical width to enable the tubes to be red successfully. If the pulse is too narrow it will not contain sufficient energy to fire a tube, and if it is too wide there is a danger of two i ln the first place, the shape of the input pulse tothe trigtubes being fired. A second disadvantage is'that a counting tube is unable to supply a satisfactory output pulse to an external circuit because its' cathode circuit is `de signed to produce a bias voltage, and is not suitable for producing pulses.

rThe connection between cathode and trigger electrodesf of adjacent tubes also gives rise to further disadvantages. The trigger electrode of a conducting tube assumes a potential between that of anode and cathode, and this is applied to the cathode of the previous tube in the chain.

If a bias were taken fromthe cathode of a counting tube to an external circuit, the variable lvoltage at the cathode due to this trigger connection will result in an unsatisfactory output. Further, because of the connection of a trigger electrode to earth through the cathode circuit of the adjacent tube, the trigger electrode tends to behaveas a second cathode, and this increases the deionisation time of the tube.

It is the object of the present invention to provide an improved counter circuit employing gas-filled` discharge tubes in which these disadvantages are overcome.

According to one feature of the invention, in a pulse rice counting circuit employing a plurality of gas-filled discharge tubes arranged to conduct successively in response to successive pulses applied to the circuit, the lconduction of a counting tube serving to extinguish an already conducting tube a permanent biasing potential is applied to all the counting tubes and the striking of a counting tube is effected by a pulse repeating arrangement having a single pulse input and outputs individual to the counting tubes, the conduction of one counting tube serving to bias the pulse repeating arrangement whereby the next pulse on the pulse input is directed to the output individual to the counting tube adjacent to said one tube to cause the striking of said second-mentioned tube.

According to another feature of the invention, in a pulse counting circuit employing a plurality of gas-filled discharge tubes arranged to conduct successively in response to successive pulses applied to the circuit, the conduction of a counting tube serving to extinguish an a1- ready conducting tube each stage of the counting circuit includes a pulse repeating tube in addition to a counting tube and a pulse source is connected in common to all the pulse repeating tubes, a pulse repeating tube of one stage receiving a biasing potential from the counting tube of the preceding stage when this counting tube is conducting to enable the pulse repeating tube to conduct on the reception of the next pulse from said source and in conducting to cause the counting tube of said one stage to conduct.

According to a further feature of the invention, in a pulse counting circuit employing a plurality of gas-filled discharge tubes arranged to conduct successively in response to successive pulses applied to the circuit, the conduction of a counting tube serving to extinguish an already conducting tube a pulse repeating tube is arranged in series between counting tubes of adjacent stages and the conduction of the counting tube of one stage serves to apply a biasing potential to the pulse repeating tube which conducts on the next pulse received from a source connected in common to all the pulse repeating tubes and in conducting causes the counting tube of the adjacent stage to conduct.

The invention will be understood from the following description of one embodiment, the circuit of which is shown in the accompanying drawing.

Referring to the drawing, a series of gas-filled discharge tubes of the cold-cathode type is arranged to form a counting chain, which in the embodiment shown has ve stages, VC1 to VCS. A second series of similar tubes VR1 to VRS is arranged to receive positive pulses from a common pulse source over lead 10.

Assuming tube VC1 to be conducting, the voltage developed across resistor R1 is applied to the trigger electrode of tube VRZ and a potential diierence now exists between the trigger electrode and cathode of this tube which is arranged to be less than the breakdown voltage of the path between these electrodes, which will be referred to as the minor gap.

A pulse .applied to the trigger electrode of tube VR2 from lead 1t) via capacitor C1 increases the voltage across the minor gap of this tube to a value greater than the breakdown voltage, and the ionisation of the minor gap causes the main gap to become conducting. The cathode potential of tube VRZ rises quickly as capacitors C2 and vC3 are charged, and from the junction point of these two 651capacitors a sharp pulse is applied to the trigger electrode `of tube VC?. via capacitor C4. The minor gap of this tube is already primed by the connection of +ve 50 v. to the trigger electrode, and the pulse from tube VRZ, therefore, causes tube VCZ to fire.

The pulse repeating tubes VRI to VRS are larranged to be self-extinguishingand after delivering a pulse to tube VCZ, tube VRZ extinguishes. The latter tube coriducts initially while capacitors C2, C3 and CS are charging, but after this initial current surge which supplies a pulse from the cathode circuit the voltage drop in the series resistors R3, R4 and RS when the minimum tube current is passing through them Vis too great to maintain the necessary voltage across .the tube, which therefore extinguishes.

When tube VC2 fires, there is an increase in the voltage developed across resistor R2, and the potential applied to the anodes of tubes VC1 to VCS is therefore reduced. Capacitor C6 is charged due to the current flow in R1, and tends to maintain a positive voltage at the cathode of tube VCl. Because of the reduction in anode voltage, the voltage across the main gap of this vtube is now insutiicient to maintain conduction, and the tube is therefore extinguished. Capacitor C7, however, is initially uncharged, and at the instant the tube commences to conduct there is still an adequate voltage existing across this main gap to maintain conduction. Each counter tube which strikes therefore causes the previously conducting tube to extinguish, and in this way the tubes in the countingy circuit are caused to conduct in turn, the conduction of one tube serving to extinguish the conducting tube of the previous stage.

The risc in potential at the cathode of tube VC2 when this tube hres is applied as a bias to tube VR3, and the latter tube will be recl by the next pulse received from lead 10.

Tubes in thc series VRI to VRS are tired on receipt of successive pulses from lead 10, and, before extinguishing, tire the corresponding counter tubes in the series VCI to VCS. The connection of the cathode of tube VCS to the trigger electrode of tube VRl causes the counter to run cyclically.

It is usual for the counter to be started at the first stage i. e. ti e urst pulse received over lead 10 ring tube VRI, which in turn fires tube VCI. To enable this t0 be done, an auxiliary tube VRSA is connected in parallel with tube VRS, and tube VRSA is arranged to be permanently primed by connection of l-ve 50 v. to its trigger electrode. A pulse applied over lead 11 to its trigger electrode will cause tube VRSA to fire, and a pulse will be applied from its cathode load to the trigger electrode of tube VCS, which in turn will re and apply a priming bias to tube VRI. The latter tube will, therefore, ,tire when the iirst pulse is received over lead 1t). An alternative method of priming tube VRI is shown, a tube VCSA being connected for this purpose in the counting tube series and sharing the cathode load of tube VCS. Tube VCSA is also permanently primed, and a pulse applied over lead 12 to the trigger electrode of this tube will cause it to tire and to apply a priming bias to tube VRl.

The cathode pulses generated by tubes VRI to VRS are available to external circuits at leads P1 to PS, and bias voltages from the cathodes of tubes VCI to VCS may be applied to external circuits over leads B1 to BS. These output biases will not be seriously affected by potential changes on the trigger electrode of the pulse repeating tube to which an output lead also has connection, because the pulse repeating tube to which this trigger electrode belongs, fires and extinguishes during the discharge time of the capacitor supplying the bias.

Provided the pulses applied to the counter via lead 10, are of sufficient amplitude to iire the minor gap of a pulse repeating tube, their width is not critical. There is no chance of a second pulse repeating tube being tired because at the time a pulse is received no pulse repeating tubes are iircd, and only one is primed. The connection of the trigger electrodes of the counting tubes to +ve 50 v. eliminates the tendency of the trigger electrodes to behave as second cathodes, and this enables a circuit with a lower time constant to be used in the cathode loads of the counting tubes. "These tubes are able to 4 de-ionise more quickly, and the counter can be driven faster.

It will be apparent that various modications are possible to the described embodiment which retain the advantages of the invention. For example, the pulse repeating tubes VRI to VRS may be connected in various ways while still fulfilling their purpose of distributing pulses from the common source to the counting tubes.

The tubes may, for instance, be extinguished by an alternating anode control voltage synchronous with the pulse input controlled, for instance, by a static switching device such as a self-extinguishing thyratron, or may be extinguished by an interruption of the H. T. supply by means, for example, of an electromagnetic relay. Further advantages may be obtained by including a tube such as VRSA or VCSA in any of the stages of the counter to enable the count to be started at a stage other than the rst. A further advantage could be gained by putting the bias voltages at the trigger electrodes of the counter tubes under the control of an external circuit, to enable the counter to be started and stopped independently of the pulses applied over lead 10.

We claim:

1. A pulse counting circuit employing cold cathode gas discharge tubes provided with an anode, a cathode and an ignition electrode and having a plurality of stages each including a rst and a second cold cathode gas discharge tube and comprising in addition a source of pulses, means connecting said source of pulses to the ignition electrodes of the first tubes of all stages, means connecting the cathode of each second tube to the ignition electrode of the first tube of the next succeeding stage, means connecting the cathode of each first tube to the ignition electrode of the second tube of the same stage and means for applying a permanent priming potential to the ignition electrodes of the second tubes of all said stages.

2. A pulse counting circuit as claimed in claim l and comprising in addition anode and cathode circuits for said rst gas discharge tubes and resistor/capacitor networks in said anode and cathode circuits whereby said first tubes are rendered self-extinguishing.

3. A pulse counting circuit as claimed in claim 1 and comprising in addition a common anode supply anda common anode resistor for said second gas discharge tubes whereby the striking of one of said second gas discharge tubes serves to extinguish any other conducting one of said tubes.

4. A pulse counting circuit as claimed in claim 1 and comprising in addition means connecting the cathode of the second tube of the last stage to the ignition electrode of the first tube of the first stage to enable cyclic yoperation to take place.

5. A pulse counting circuit as claimed in claim 1 and comprising in addition a further tube, a common cathode load for said further tube and the second tube of one of said stages and means independent of said source of pulses for striking said further tube whereby to determine a starting point for the counting operation.

6. A pulse counting circuit as claimed in claim 1 and comprising in addition a further tube, a common cathode Vload for said further tube and the first tube of one of said stages and means independent of said source of pulses for striking said further tube whereby the counting tube of said one stage strikes to determine a starting point for the counting operation.

References Cited in the tile of this patent UNITED STATES PATENTS 2,668,931 Hall et al. Feb. 9, 1954 2,678,409 Holden May ll, 1954 2,709,771 Dehn May 3, 1955 2,719,250 Six et al. c.. Sept. 27, 1955 2,739,265 Six et a1. Mar. 20, 1956 

